AutoFocus User’s Guide
53
©1989-2018 Lauterbach GmbH
How to understand A.ShowFocusEye and A.ShowFocusClockEye
The
Analyzer.ShowFocusClockEye
window is frequently confused with the
Analyzer.ShowFocusEye
window. Both windows show similar graphs, but contain absolutely different information.
The following figures show the resulting sample clock signal in dependency of the clock threshold level
setup:
The threshold can be set manually using the command
Analyzer.ThresHold
<value>
or automatically with
the command
Analyzer.ThresHold Clock
. The algorithm attempts to find a threshold level close to a duty
cycle of 50/50 as seen in the figure B.
Important to know
: The clock threshold level influences the data setup (Ts) and hold (Th) times in
dependency of the clock waveform. The higher the trace port data rates are, the more attention you must
pay to this effect.
NOTE:
The dimensions of both, the data eyes and the clock waveform, do highly
depend on the clock threshold level.
NOTE:
It is possible to change the data setup and hold times through the clock
threshold level. But this is not the right way to compensate for data or clock
skew.
However, this effect sometimes is the last option to get a suitable trace listing.
Target clock
Clock threshold
Resulting sample clock
Fig.A
Fig.B
Ts
Th
Ts
Th
Ts > Th
Ts < Th
Target clock
Clock threshold
Sample clock
Data
Timing
Sample clock
